Bioreactor temperature control using modified fractional order IMC-PID for ethanol production

The product quality of a fermentation process depends on a number of factors such as temperature, pH, nutrient balance, dilution rate, dissolved oxygen and CO₂ concentration etc. The present work focuses on the precise temperature control of the process and to achieve desired product quality. Therefore a novel control algorithm, which is an amalgamation of fractional mathematics and IMC-PID, having less design parameters is proposed. A fractional order IMC-PID is designed and then modified (MFOIMC-PID) by incorporating an extra control loop with proportional gain to reduce the offset error. A nature inspired optimization technique i.e. water cycle algorithm is utilized for estimation of optimum design parameters of proposed controller which leads to WMFOIMC-PID controller. Fractional order PID (FOPID) and conventional PID are also designed for comparative study. Simulation results show that the proposed controller reduces integral absolute error (IAE) by 57% and 72% in comparison to FOPID and PID respectively for set-point tracking. Similar reduction of IAE is observed for disturbance rejection and noise suppression. Thus WMFOIMC-PID proves to be more robust and efficient in comparison to the other designed controllers.